1. Field of the Invention
The present invention relates to. a process for the preparation of lithium-calcium grease compositions.
2. Description of the State of the Art
Lithium-calcium grease compositions have existed in the art for many years. These greases are traditionally prepared in sealed autoclaves where the ingredients are subjected to high temperatures and pressures during the cooking step. The resulting products are often inconsistent in quality due to over or under dehydration of the calcium soap portion of the grease and demonstrate poor mechanical stability and lack of batch to batch uniformity. It has been shown that in both open kettles and in sealed autoclaves, calcium soaps dehydrate readily and will not subsequently disperse into the required fibrous structure after being even mildly dehydrated. This dehydration, which causes the calcium soap to precipitate rather than disperse in the grease, reduces its ability to thicken the grease. The precipitated calcium soap cannot be re-dispersed even under vigorous milling (grinding/dispersing) conditions, nor can it be rehydrated by adding water, even at lower temperatures.
Additionally, the temperatures required for making lithium soap greases are over 100.degree. F. higher than generally allowed for calcium grease. Thus, during the heating cycle with sealed autoclaves, the only water vented is that used to suspend and disperse the lithium and calcium hydroxides and then the autoclave is sealed to try to retain the remaining water for the water of crystallization of the calcium soap.
It is desirable to have a process which provides for proper lithium soap formation without completely dehydrating and precipitating the calcium soap, which process also produces greases of consistent quality and good mechanical properties.